The thermodynamic method used in nearly all air conditioners, refrigerators and heat pumps is the vapor compression cycle also called the refrigeration cycle. The basic cycle uses four primary components: a compressor, a condenser, an expansion device, and an evaporator; some systems may use additional components such as a receiver, additional heat exchangers, two or more compressors, and/or an accumulator and other specialized components such as a liquid-vapor separator or a vortex separator and/or a surge tank or refrigerant reservoir or vessel. The four primary components are piped in series to form a closed loop system that carries out the changes in temperature, pressure and state of the working fluid refrigerant that form the basic vapor compression cycle. Furthermore, within air conditioners, refrigerators, and heat pumps outside of the refrigeration cycle there are typically ancillary components that move the desired heat transfer medium, such as the blowing of air or of flowing of water that is to be cooled or heated, across the primary heat exchangers being the condenser coil and the evaporator coil. In addition there is typically a control circuit that energizes and de-energizes the driven components including the compressor and such as fan motors, pump motors, damper actuators, and valves accordingly to meet a desired temperature, ventilation and/or humidity or other set points and operating parameters.
The present invention makes adjustments to an air conditioning, refrigerating or heating system for the purpose of maximizing measured EER, COP and/or IEER in a feedback loop utilized to optimize cooling or heating capacity relative to power consumed. The efficiency of vapor compression cycles is numerically described by an energy efficiency ratio (EER) and/or a coefficient of performance (COP). The EER generally refers to the air conditioning, refrigerating or heating system and is the ratio of the heat absorbed by the evaporator cooling coil over the input power to the equipment, or conversely for heat pumps, the rate of heat rejected by the condenser heating coil over the input power to the equipment. EER is defined as the ratio of cooling or heating provided to electric power consumed, in units of Btu/hr per Watt. EER varies greatly with cooling load, refrigerant level and airflow, among other factors. The COP generally refers to the thermodynamic cycle and is defined as the ratio of the heat absorption rate from the evaporator over the rate of input work provided to the cycle, or conversely for heat pumps, the rate of heat rejection by the condenser over the rate of input work provided to the cycle. COP is a unitless numerical ratio. In addition, there is a standard weighted average of EER at four conditions known as the integrated energy efficiency ratio (IEER), which relates to an estimation of the energy efficiency over conditions experienced during a cooling season. Also, there is the seasonal energy efficiency ration (SEER) that is used instead of the IEER for smaller air conditioning units. Either effect of lowering capacity or increasing power manifest in reduced energy efficiency and a reduced EER, COP and IEER while making adjustments to increase capacity without increasing power, or reducing power without decreasing capacity, or both increasing capacity and reducing power will manifest in an increased EER, COP and IEER.
The actual operating EER or COP is key to maximizing efficiency, because it provides an absolute, realistic and continuous assessment of operational efficiency with feedback so a harmonized adjustment of operating parameters can be conducted. Measuring the EER, COP and IEER of systems based on the vapor compression cycle is difficult, more so while operating in a field environment rather than a test laboratory. An accurate heat absorption or heat rejection measurement for these systems is quite complex and requires measurement of the mass flow rate of fluid through the heat exchanger along with enthalpies entering and leaving the heat exchanger; a detailed description of EER and COP measurement is provided for a related invention that is disclosed separately.
The measured EER and COP are affected by the load under which the air conditioning, refrigeration or heating system is running; the load is a function of the evaporating and condensing temperatures. An increase in evaporating temperature will raise the measured EER and COP, as will a decrease in condensing temperature; as can be predicted by the thermodynamic cycle parameters. Likewise, lower evaporating temperature will reduce the measured EER and COP, as will higher condensing temperature.
The prior art does not make adjustments to the operating parameters or the components of the air-conditioning, refrigeration or heat pump system according to the measured EER or COP, neither to increase the evaporating temperature or decrease the condensing temperature, nor to adjust other parameters that effect the refrigerant subcooling or superheat, or the refrigerant composition in the case of systems using mixtures of two or more refrigerants, or of the refrigerant mass flow rate, or the refrigerant pressures, to maximize the EER or COP. An energy management system for refrigeration systems by Cantley (U.S. Pat. No. 4,325,223) relies on inference of energy efficiency rather than a direct measurement; the inference is based on relative comparison of compressor power data and other system parameters stored in memory; and the system does not make control adjustments according to the system energy efficiency ratio, rather it controls evaporative cooling. An invention by Spethmann (U.S. Pat. No. 4,327,559) applies to chilled water systems rather than direct expansion (DX) systems; and simply balances the trade-off between colder chilled water versus faster fan airflow using ratio relays. A method by Enstrom (U.S. Pat. No. 4,611,470) also applies only to chilled water systems; the described method for performance control of heat pumps and refrigeration equipment depends on the chilled water temperature and does not mention refrigerant temperature or pressure measurements. The purpose of an invention by Bahel, et al. (U.S. Pat. No. 5,623,834) is diagnostics and fault correction, rather than energy efficiency optimization; and only the fan speed and thermostatic expansion valve are controlled based on relative comparison of two temperatures and the thermal load calculated via a thermostat. Two patents by Cho, et. Al (U.S. Pat. No. 6,293,108) disclose methods for separating components of refrigerant mixtures to increase energy efficiency or capacity, however, energy efficiency ratio is neither measured nor is it a basis for adjustments. Chen, et al. (U.S. Pat. No. 7,000,413) discloses control of a refrigeration system to optimize coefficient of performance, yet there is no detailed description of how COP is calculated. Adjustment is carried out to achieve a reference COP stored in memory rather than being an optimization process. Also, the primary application of Chen, et al. is transcritical systems using carbon dioxide refrigerant; an embodiment for measurement of the refrigerant flow rate is not described; and only water flow rate and the expansion valve are adjusted. Automatic refrigerant charge adjustment methods by Kang, et al. (U.S. Pat. No. 7,472,557), Murakami, et al. (U.S. Pat. No. 8,056,348), and McMasters, et al. (U.S. Pat. No. 8,272,227) simply adjust charge to match published charging tables or reference temperature or pressure values, which are not optimized values, rather they are non-optimal compromise values that work under a wide range of operating conditions and load.